The present invention relates to a process for forming stable moldable and molded products and more particularly to a process and apparatus for forming stable moldable and molded products from a granular scrap material, such as reground rubber, and a cohesive base material, such as a thermoplastic rubber.
Plastics may be formed and subsequently molded into useful articles by a variety of methods. For example, in extrusion processes, a polymer may be propelled continuously along a screw through varying regions of high temperature and pressure such that the polymer is melted and compacted and finally forced through a die shaped to give the final object. The molding of thermoplastic materials may likewise be accomplished by a number of devices and methods, including injection molding. In an injection molding process the polymer is generally preheated in a cylindrical chamber to a temperature at which it will flow and then forced into a relatively cold closed mold cavity by means of high pressures applied through a plunger. A reciprocating screw may be employed to deliver the feed to the mold. A brief description of these processes may be found in Billmeyer, Text Book of Polymer Science (2d Edition, 1971), pp. 492-498.
Extruders have been employed to form plastic compound, including various kinds of recycled rubber. For example, U.S. Pat. Nos. 4,003,408 and 4,110,420, issued to James E. Turner describe an apparatus including an extruder to form a porous pipe made primarily of rubber and synthetic rubber reclaimed from rubber tires. U.S. Pat. No. 3,386,925 issued to Dillhoefer makes reference to injection molding and extruding of a thermoplastic rubber blend comprising reclaimed rubber, and U.S. Pat. No. 2,809,944 issued to Sverdrup makes reference to the use of a screw impeller in processing a reclaimed rubber by joint working and admixture of a vulcanized rubber scrap and a thermosetting phenol-formaldehyde resin at a temperature within the rubber-reclaiming range.
The patent literature discloses a variety of processes which attempt to process a reclaimed rubber. For example, U.S. Pat. No. 4,028,288 issued to James E. Turner discloses a heat and pressure molded end product made of a mixture of particalized rubber tires and a lesser amount of a synthetic resin thermoplastic material. The porosity of the molded end product is controlled by the amount of rubber material bits mixed in the precursor material. Thus, it is stated that a 50-50 rubber-plastic mixture results in an end product with very little porosity, while an 80-20 rubber-plastic mixture results in a very porous end product.
U.S. Pat. Nos. 4,110,420 and 4,003,408, also issued to James E. Turner, disclose a method and pipe product made primarily of rubber and synthetic rubber reclaimed from rubber tires. The rubber and synthetic rubber are ground to a relatively small size, and process mixed through a pipe extruder with a smaller amount of a binder mix of primarily polyethylene, along with vinyl, ABS binder, and a trace of attaclay. A porous pipe said to be useful in underground irrigation is formed.
U.S. Pat. No. 3,386,925 issued to Dillhoefer discloses a blend which may be formed by injection molded extrusion and other processes. The blend is made of a copolymer of ethylene and vinyl acetate containing from 12 to 25 weight percent based on the copolymer of vinyl acetate and a reclaimed rubber with certain characteristics. The copolymer is present in a concentration of 20-85 weight percent based on the blend. Reclaimed rubber is defined as the depolymerization product of vulcanized comminuted rubber which retains at least in part the cross links imparted by the vulcanization process of the original rubber.
Other patents disclose reclaimed rubber compositions, such as U.S. Pat. No. 2,437,538 or processes for reprocessing reclaimed vulcanized rubber, such as U.S. Pat. No. 2,809,944, wherein there is disclosed a process for forming certain products from vulcanized rubber scrap, such as scrap from tires and a thermosetting phenolformaldehyde resin by mixing the resin with the vulcanized rubber and reclaiming the rubber by plasticizing the materials in admixture by a joint working at a temperature within the rubber-reclaiming range followed by subsequent curing under vulcanizing conditions. The plastic may be in the range of from 5 to 15% of the vulcanized rubber product.
A variety of other processes have been disclosed utilizing old rubber particles. For example, U.S. Pat. No. 2,240,015 discloses a process whereby a dispersed emulsion of old rubber particles is sprayed on a surface and then baked. Similarly, in U.S. Pat. No. 2,723,934 there is disclosed a porous rubber material made from vulcanized rubber with an adhesive reinforcing substance added in the interstices of the rubber.
There is a reference in the advertising literature to using copolymers for upgrading recycled and scrap material. More particularly, in a technical bulletin from the Shell Chemical Company entitled "Shell Kraton.RTM. Rubber for Modification of Thermoplastics," No. SC:165-77 (February 1977) it is stated that Kraton rubbers may be used for general upgrading of recycled and scrap material.
These and other prior processes have suffered from one or more defects and limitations. For example, the percentage of scrap rubber which may be employed is often limited depending upon the properties of the end product. For example, plastics formed from a mixture of recycled rubber having more than 50% by weight recycled rubber have generally not had uniform properties. Additionally, various processes using recycled materials result in products having other unacceptable properties. These and other limitations and defects are substantially minimized if not eliminated by the present inventive process and method.